Electromagnetic radiation absorbing surfaces are well known. Such electromagnetic radiation absorbing surfaces are utilized in electromagnetic radiation test cells such as those commonly used in electromagnetic compatibility (EMC) and electromagnetic interference (EMI) testing. They are also utilized in electromagnetic anechoic chambers for testing high-frequency radar, antennas, and in low observable structures. The increase in consumer electronics which broadcast electromagnetic radiation, such as cellular telephones and portable computers, has enhanced the need for techniques and materials which suppress stray electromagnetic radiation, particularly in airplanes and near airports so as to prevent interference with airport radar, communications, and automated landing systems. Buildings may incorporate such material to mitigate the intensity of unwanted electromagnetic radiation therein.
As will be appreciated by those skilled in the art, it is often necessary to measure the effectiveness of such electromagnetic absorbent materials. Thus, it is necessary to provide an accurate means for measuring the ability of a material to absorb electromagnetic radiation.
In this regard, it is known to position an electromagnetic transceiver proximate a test surface, radiate electromagnetic radiation from the transceiver to the test surface, and measure the electromagnetic radiation reflected therefrom. Of course, the intensity of the electromagnetic radiation reflected from the test surface will be inversely proportional to the ability of the test surface to absorb electromagnetic radiation.
However, such contemporary methodology suffers from inherent deficiencies. For example, frequently it is desirable to measure electromagnetic radiation absorption at various different locations (x-y positions) upon the test surface. It may be desirable to measure electromagnetic radiation absorption at one or more points upon the surface, along a line upon the surface, or at regularly spaced points defining an array upon the plane of the surface. In such instances it is frequently desirable to provide precise positioning of the electromagnetic transceiver, so as to accurately provide for electromagnetic radiation absorption measurements at the desired locations.
As those skilled in the art will further appreciate, it is also desirable to precisely position the electromagnetic transceiver vertically (along the z-axis thereof), so as to enhance the accuracy of measurements made therewith. It is well known that the output of an electromagnetic transceiver varies substantially due to phase differences between the electromagnetic radiation transmitted and that received thereby. Destructive interference between the transmitted and received electromagnetic radiation causes variations in the measured intensity of the received electromagnetic radiation according to well known principles. As such, it is desirable to maintain a constant phase difference between the transmitted and reflected electromagnetic radiation. For example, since the output of the electromagnetic transceiver is maximum when the transmitted and reflected electromagnetic radiation are in phase, then it is frequently desirable to maintain such in-phase relationship between the transmitted and received electromagnetic radiation and thus enhance the accuracy of electromagnetic radiation absorption measurements.